1. Field
The disclosure relates to a regenerative braking system, and more particularly to a regenerative braking system capable of charging a battery with regenerative energy through regenerative braking upon the braking operation for a vehicle.
2. Description of the Related Art
A regenerative braking system is a core technology for an electric car driven by electric energy, such as an HEV (hybrid electric vehicle), an EV (electric vehicle), and an FCEV (fuel cell electric vehicle).
Different from the normal braking system, in which kinetic energy of the vehicle is converted into frictional heat energy, the regenerative braking system drives a motor by using the kinetic energy and charges a battery with electric energy generated from the motor in order to increase the driving distance and improve the driving efficiency of the HEV, EV and FCEV, so that the regenerative braking system is essential to improve the fuel consumption ratio.
When the braking operation for an electric vehicle equipped with the regenerative braking system is performed, a driver must determine the priority between the regenerative braking and the normal frictional braking according to the driving state of the vehicle and the intention of the driver. In addition, if the regenerative braking and the normal frictional braking are simultaneously performed, the power of the regenerative braking and the normal frictional braking must be controlled. The energy recovery rate may become increased as the proportion of the regenerative braking is increased, but the regenerative braking must be restrained depending on the charge state of the battery, the motor temperature, etc. If the power of the regenerative braking is not properly controlled, the motor or the battery may be damaged. In contrast, if the power of the regenerative braking is insufficient, the power of the normal frictional braking must be increased to satisfy the demand of the driver for reducing the vehicle speed.
Therefore, a regenerative braking system employing a conventional hydraulic brake system is used for a soft type electric vehicle having a low-capacity motor. In addition, since the proportion of the regenerative braking and the normal frictional braking is fixed according to the vehicle speed, the amount of regenerative energy retrieved to the battery may be limited.
In addition, the regenerative braking system employing the conventional hydraulic brake system may cause uncomfortable feeling during the braking operation if the regenerative braking transient occurs due to the difference in responsiveness between the hydraulic braking force of the hydraulic brake and the regenerative driving force of the driving motor.